In my U.S. Pat. No. 4,500,103 for a HIGH EFFICIENCY BICYCLE FRAME, very large diameter frame tubing is used in a bicycle to resist relatively large torsional and bending forces to produce a bicycle which is very light in weight yet extremely rigid and which, at the same time, provides an extremely good ride. In my U.S. Pat. No. 4,621,827. I disclose a bicycle in which the chainstay tubes are made of unequal rigidity and made in such a way so as to increase the power train efficiency by reducing the magnitude of frame deflection caused by chain stress. The present invention is directed to improvements in the steering and front fork assembly head set bearing and handlebar stem of a bicycle.
The front fork of bicycles typically have been steel with about one inch steerer (e.g., one inch outside diameter steerer post in steel). That is what the headset bearings and all the headset pieces were made to accommodate and the one inch size was limiting in steel. The steel steerer uses a fairly thick wall near the crown in order to make the fork strong enough.
In the bicycle described in my U.S. Pat. No. 4,621,827, the head tube had an outside diameter of about 1.42 inches and an inside diameter of about 1.180 and a center section wall thickness of about 0.065 inches. In order to fit in one inch bearing size constraint in aluminum, a solid bar had to be used and it still is not strong enough because of the small diameter size.
In the past, on mountain bikes and on some road bikes, others have started promoting larger headset sizes with 11/4 inch steering tubes. This is still made of steel in order to make the forks more rigid for better cornering control but they are still essentially about the same weight or heavier. There have been suggestions of aluminum forks. These use a conventional headset and headset bearing units. Hence, the front fork and headset assembly of a bicycle has been the heavy end of the bike and it has been the end that gets the most shock.
There has been introduced to the market a number of front forks which do not have curved blades but which have instead straight blades and there is controversy in the bicycling art concerning whether these straight blades provide harsher riding forks or not. The present invention uses straight blades.
The wheel axle is typically offset forward of the steering axis in order to obtain desirable handling. This offset is called the fork rake. The present invention uses a fork rake of about 11/2 inches.
Headset bearing failures are a frequent problem in off-road bicycles. The repeated impacts of off-road use brinell the bearings, loosen the bearing housings in the head tube and the fork crown, loosen and damage the threaded adjustment mechanism. Because of angular misalignment tolerances necessary for inexpensively machined steerer crowns, head tubes and adjusting threads, the traditional bearing assemblies use a cup and cone system, where the radius of curvature of the balls is much smaller than that of at least one of the raceways. This allows the bearing to tolerate angular misalignment and substantially reduces the contact area of the balls, compared to the Super Conrad style bearing--with raceways closely fitted to the balls. The rigidity of the point contact style bearings is thus substantially lower than that of the torque tube type bearing and the load carrying capacity is very much lower. This invention is able to fully utilize the advantages of double-sealed aircraft torque tube type bearings by machining the outside diameter of the steering tube for direct fit and adhesive bonding of the headset bearings to the external surfaces of the steering tube and raceway seats in the head tube, insuring accurate alignment. The ends of the head tube are also precision bored for alignment, and also benefit from direct fit. The threaded adjustment of traditional headsets is another source of trouble. The threads weaken the thin wall steering tube and can break there, especially if the handlebar stem is clamped inside the threads.